The present invention relates to optical tactile sensors, sensing methods using optical tactile sensors, sensing systems, methods and apparatuses for controlling object operating force, apparatuses for controlling object gripping force, and robot hands.
Although a society where humans and humanoid robots coexist side by side is becoming more realistic, there remain a number of problems to be solved first. While improving the maneuverability and the intelligence of robots is of great importance for this purpose, improving the technology for allowing communication between humans and robots is also thought to provide a shortcut to a society where humans and robots can coexist.
What is central to such communication technology is remote control of robots that perform tasks under human direction. In the field of remotely controlling robots, a key technology for smoothly executing tasks includes sensing tactile information with tactile sensors. One exemplary technology being contemplated is that of sensing the weight and the coefficient of friction of the object (to be handled) and adjusting the gripping force of the robot hand based on the weight and the coefficient of friction sensed. Such gripping force adjustment is expected to allow the robot to grip objects without damaging or dropping them.
Also contemplated has been application of the same principle for sensing an object's friction coefficient (slip) to a tactile sensor as that used in human fingertips so as to facilitate sensing the slip by the sensor (see, for example, Hiromitsu, S. and Maeno, T.: “Stick/slip Distribution on the Fingerpad and Response of Tactile Receptors when Human Grasp an Object,” The Japan Society of Mechanical Engineers, Vol. 68, No. 667 C: 914-919(March 2002). This document discloses the principle of detecting the slip (coefficient of friction) of an object by extracting a “fixed region” and a “slip region” within the region of contact between the object and the tactile portion of the robot hand.
A conventional sensor of this type that employs this principle includes a mechanical tactile sensor with a plurality of strain gauges arranged within elastic curved bodies for measuring the pressure distribution or the distribution of distortion within the elastic bodies based on the output of each strain gauge so as to determine the slipperiness and fixedness of the object (see, for example, Japanese Published Unexamined Patent Application No. 2000-254884).
Another type of a conventional sensor is an optical tactile sensor that captures the deformation of a clear elastic object with imaging means, such as a CCD camera. This can be achieved, for example, by embedding layers of spherical markers in a clear elastic body shaped into a rectangular parallelepiped and measuring the displacement of each marker with a CCD camera so as to measure the three-dimensional force vector and torque that occur approximately on the contact region (see, for example, Japanese Published Unexamined Patent Application No. 2000-523568 and Kamiyama, K., Kajimoto, H., Inami, M., Kawakami, N., and Tachi, S.: “Development of A Vision-based Tactile Sensor,” IEEJ Trans, SM, Vol. 123.No. 1, 16-22(2003)).
One problem associated with the mechanical tactile sensor is its insufficient durability, since it performs sensing by allowing the strain gauges to be deformed. Moreover, as a plurality of strain gauges need to be arranged within an elastic body, the manufacturing of the sensor may become complicated or the wiring may become difficult.
On the other hand, in the above-described optical tactile sensor, as the surface of contact with the clear object (to be gripped) is flat, it is difficult to detect the coefficient of friction between the object and the sensor's tactile portion. Furthermore, providing curvature for the above-mentioned surfaces of contact, if attempted, would be extremely difficult.
Additionally, a finger-like tactile sensor has been proposed. However, such a finger-like sensor can only measure the state of contact and the contact pressure, thus being incapable of simultaneously measuring multi-dimensional mechanical quantities, including the coefficient of friction.
A combination of different types of tactile sensors, i.e., mechanical tactile sensors and optical tactile sensors, has been proposed as a means for measuring multi-dimensional mechanical quantities (see Hiromitsu, S. and Maeno, T.: “Stick/slip Distribution on the Fingerpad and Response of Tactile Receptors when Human Grasp an Object,” The Japanese Society of Mechanical Engineers, Vol. 68, No. 667 C: 914-919(March 2002)). However, such a sensing means would not be amenable to size-reduction since it requires two different types of sensors.
One object of the present invention, which has been made in view of the foregoing problems, is to provide an optical tactile sensor that can be easily manufactured and reduced in size. Another object of the present invention is to provide a sensing method and system, a method and apparatus for controlling object operating force, an apparatus for controlling object gripping force, and a robot all equipped with one type of optical tactile sensors which simultaneously sense different mechanical quantities in an exemplary embodiment.